Eight foreign troops and a contractor have been killed by an Afghan air force pilot at Kabul airport in an apparent argument, Nato says. The incident took place at a facility used by the Afghan air force at about 1100 local time (0630 GMT), the Afghan defence ministry said. The pilot was also killed in the exchange.The incident is the deadliest of a number of recent attacks on foreigners by Afghan security personnel.“We can confirm there was small-arms fire during this incident,” said Nato-led International Security Assistance Force spokesman Maj Tim James. In the past two years, 42 foreign troops have died at the hands of Afghans they were mentoring, or Taliban dressed in police or army uniform. These incidents resonate widely, and are bad for morale. American and British soldiers say that they must remain on their guard - that they can never fully trust the Afghan soldiers and police they serve with. “We don’t know how the shooting started.”The nationalities of the dead have not been divulged pending notification of their families. Witnesses reported hearing sirens and seeing a heavy military presence near the facility, which generally has tight security. A senior Afghan security official told the BBC the pilot’s name was Gul Ahmad, and he came from the Tarakhel area of Kabul.He was suffering from “mental illness”, and either got into a fight with his foreign colleagues or planned the attack after being recruited by the Taliban, the official said. The Taliban claimed responsibility for the incident in a text sent to the Associated Press news agency, but the authorities have not confirmed any insurgent activity. Correspondents say rapid recruitment into the Afghan military has raised fears of Taliban infiltration into the police and army.Nato’s exit strategy for Afghanistan involves progressively handing over to the local security forces. Until now the deadliest of the recent attacks on foreign troops was last November when an Afghan policeman killed six US soldiers.And two Nato soldiers were shot dead by an Afghan border policeman in northern Faryab province on 4 April, local officials said.The BBC’s Quentin Sommerville in Kabul says foreign troops broadly but not totally trust their Afghan colleagues and feel they have to keep half an eye on them.The attackers are sometimes actually members of the Afghan security forces, and sometimes insurgents impersonating servicemen.